The development of English language learners (ELLs) was explored from kindergarten through eighth grade within a nationally representative sample of first-time kindergartners (N = 19,890). Growth curve analyses indicated that, compared to native English speakers, ELLs were rated by teachers more favorably on approaches to learning, self-control, and externalizing behaviors in kindergarten and generally continued to grow in a positive direction on these social/behavioral outcomes at a steeper rate compared to their native English-speaking peers, holding other factors constant. Differences in reading and math achievement between ELLs and native English speakers varied based on the grade at which English proficiency is attained. Specifically, ELLs who were proficient in English by kindergarten entry kept pace with native English speakers in both reading and math initially and over time; ELLs who were proficient by first grade had modest gaps in reading and math achievement compared to native English speakers that closed narrowly or persisted over time; and ELLs who were not proficient by first grade had the largest initial gaps in reading and math achievement compared to native speakers but the gap narrowed over time in reading and grew over time in math. Among those whose home language is not English, acquiring English proficiency by kindergarten entry was associated with better cognitive and behavioral outcomes through eighth grade compared to taking longer to achieve proficiency. Multinomial regression analyses indicated that child, family, and school characteristics predict achieving English proficiency by kindergarten entry compared to achieving proficiency later. Results are discussed in terms of policies and practices that can support ELL children's growth and development. (Contains 5 tables.)